Could global warming be changing shrimp spawning?

Monday

Dec 17, 2007 at 11:36 AMDec 17, 2007 at 11:46 AM

JOHN DeSANTIS Senior Staff Writer

THIBODAUX -- Alongside the delayed appearance of waterfowl to southern climates, droughts and forest fires, shifts in the sexual behavior of shrimp may be added -- perhaps -- to early signs of global warming.

The jury is still officially out, and so far no authoritative scientific work on the subject exists. The evidence is purely anecdotal.

But the appearance of white shrimp bearing fertilized eggs in waters where they are not historically found certainly has some scientists wondering.

"One of things we are seeing is with white shrimp, more and more gravid white shrimp in inside water," said Martin Bourgeois, the biologist who heads up Louisiana’s shrimp-management program, explaining that the shrimp are "almost exclusively in outside waters."

After breeding in the Gulf’s warm waters, shrimp do not generally swim back to inside waters.

But now, "we are seeing it, and fishermen are reporting it," he said.

Sister Lake, Lake Pelto and Lake Barre -- all familiar inshore names to local shrimpers -- are among the areas where samplings are showing egg-bearing white shrimp. No observations have been made in Lake Boudreaux, although that wouldn’t surprise Bourgeois.

He said he has no interest in entering the ongoing scientific debate over global warming and notes that increased salt content of local inshore waters may on the surface be a more definitive and explainable cause.

The presence of shrimp, death of trees and increased numbers of freshwater fish in brackish waters that for some time have been more salty than fresh is nothing new. In Lake Des Allemands, for example, where the environment is usually more prone to the appearance of catfish, crappie and other freshwater finfish, anglers have reported more runs of redfish and trout, clearly attributable to the saltier environment.

The Gulf of Mexico’s warmth is generally conductive to shrimp spawning. Local white shrimp are hatched from eggs on the Gulf tide, which carries the newborns to the marshes and interior bayous for hatching and development. As they get bigger, the shrimp head back to the Gulf to begin the cycle anew.

A result of the phenomenon mentioned by Bourgeois is that bigger white shrimp may now be found in greater numbers in waters closer to shore, which can be a boon for shrimpers who get a better price for the larger specimens.

While definitive research on links between global warming and shrimp behavior is lacking, evidence of environmental change is apparent in the actions of other life forms.

A New York Times article published last week notes later arrivals of some waterfowl along the Mississippi flyway, the route taken above the river’s valley toward warmer winter spots that affects hunting seasons in various states, including Louisiana.

In that story, scientists noted northward movement of red foxes, earlier nesting for more than two dozen types of birds and documented changes in the breeding patterns of some squirrels and frogs in both the U.S. and Canada.

Donald Boesch, professor of marine science at the University of Maryland’s Center for Environmental Science, has done extensive research on erosion of Louisiana’s coast and is well aware of saltwater intrusion’s effects on wildlife and people.

A strong proponent of global-warming theories -- he notes the Intergovernmental Panel on Climate Change’s contention that evidence of human-caused global warming is "unequivocal" -- Boesch is cautious when asked about the potential effect on shrimp.

"I think we can hypothesize about it, but I don’t know of any published literature that would support any suggestion of early maturation," said Boesch, former director of the LUMCON marine-research center in Cocodrie.

His own experience regarding the effects of climate change on marine life is limited to anecdotal evidence in the Chesapeake Bay, causing him to opine that the existence of a link between global warming and shrimp behavior is reasonable.

"We are in a more northerly climate and don’t have a shrimp fishery, though occasionally you catch some paeneid shrimp," Boesch said. "On the other hand we have species like soft clams coming from the north at the end of their range. The soft clam populations are stressed and may be dying out as the bay warms slightly. You might in the long run see a shrimp fishery in Chesapeake Bay."

While such a phenomenon could be a long way off, Louisiana’s wildlife officials are certain that the warming trends will have an effect on how shrimp are managed in the future.

"The challenges may be daunting," Bourgeois said. "From the management perspective that may mean some changes in seasonal dates and geographic changes, far in the future. We may need enabling legislation, and help from the shrimp industry. We will need everyone to pull together."

Senior Staff Writer John DeSantis may be reached at 448-7614 or john.desantis@dailycomet.com.